Jeff Masters reviews that "holy shit! greenland glaciers are melting faster!" paper...
Glaciers in southern Greenland are flowing 30% to 210% faster then they were ten years ago, and the overall amount of ice dumped into the sea from Greenland increased from 90 cubic km in 1996 to 224 cubic km in 2005, up 250%. As a result, Greenland's contribution to average annual sea rise increased from .23 mm/year in 1996 to .57 mm/year in 2005, and now accounts for between 20% and 38% of the observed yearly global sea level rise. Two-thirds of Greenland's contribution (.38 mm/yr) was due to glacier dynamics (chunks of ice breaking off and melting), and one-third (.19 mm/yr) from melting. These were the results of a paper called "Changes in the Velocity Structure of the Greenland Ice Sheet" published last Friday in Science magazine. NASA scientist Eric Rignot and University of Kansas researcher Pannir Kanagaratnam used ten years of satellite radar interferometry data to arrive at their conclusions.
The authors attributed the speedier glacier flow in southeast Greenland to climate warming, and noted that there had been a 3° C rise in temperature in the past 20 years at one station there. Widespread glacier acceleration affected just the southern tip of Greenland south of 66° north between 1996 and 2000, then spread rapidly northwards to 70° north by 2005 to cover the southern half of Greenland. The authors anticipated that as glacier acceleration continued to spread northward, Greenland's contribution to global sea level rise would continue to increase in coming years.
(...)
The consensus view (Gregory et. al, 2004), using computer models that treat the Greenland ice sheet as a static hunk of ice, has been that the Greenland ice sheet will melt in about a thousand years, if atmospheric CO2 doubles. However, the doubling in glacier flow observed in the past ten years comes as a major shock. The models used to come up with the 1000 year estimate do not account for changes in glacier speed at all! The unexpected increase in glacier flow probably occurred in response to the lubrication effect of melt-water penetrating down to the glacial bed, as well as other poorly-understood processes. The paper concluded: "Current models used to project the contribution to sea level from the Greenland Ice Sheet in a changing climate do not include such physical processes and hence do not account for the effect of glacier dynamics." In other words, the models were wrong.
Climate change skeptics are fond of criticizing computer models, and cite their inadequacy as grounds for dismissing the threat of climate change. Well, it works both ways. Climate change models can be off in the wrong direction--as we also saw with the Antarctic ozone hole, which was completely missed by the models. These new results imply that if Greenland warms significantly (at least 3° degrees C), Greenland's ice could melt in a few centuries, not 1000 years. With 20 feet of sea level rise locked up in its ice, sea level rises well beyond the capability of humans to handle could occur later this century. The real test of the stability of the Greenland Ice Sheet will come when we reach temperatures not seen since before the last ice age, 125,000 years ago. Warm temperatures then caused the Greenland Ice Sheet to mostly disintegrate, leading to perhaps 14-17 feet (4.5-5 meters) of sea level rise (Cuffey and Marshall, 2000). The likelihood of this scenario is highly uncertain, though, given our lack of understanding of the system, the high amount of natural variability, and the limited amount of historical data we have to look at.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=307&tstamp=200602
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